Throw exception if all ctor params are null

svn path=/trunk/; revision=490

src/jsr311-api/src/javax/ws/rs/core/Variant.java

diff --git a/src/jsr311-api/src/javax/ws/rs/core/Variant.java b/src/jsr311-api/src/javax/ws/rs/core/Variant.java
index b8df85c..5d5b3c1 100644
--- a/src/jsr311-api/src/javax/ws/rs/core/Variant.java
+++ b/src/jsr311-api/src/javax/ws/rs/core/Variant.java
@@ -42,6 +42,8 @@
      * null
      */
     public Variant(MediaType mediaType, Locale language, String encoding) {
+        if (mediaType==null && language==null && encoding==null)
+            throw new IllegalArgumentException();
         this.encoding = encoding;
         this.language = language;
         this.mediaType = mediaType;